Plant owner Tokyo Electric Power Co. (TEPCO) said the pair, who worked as control room operators, were the first men to surpass the government-set limit.

TEPCO said the workers were not exhibiting any immediate health problems. They had both been working at the nuclear power plant since the devastating March 11 quake and tsunami cut power to the plant and crippled cooling systems.

Without the cooling systems, fuel rods inside several reactors partially melted, sparking explosions and releasing radiation into the atmosphere.

Workers have since doused the reactors and fuel rod pools with water to stop them from overheating and releasing far greater amounts of radiation.

TEPCO hopes to bring the plant into stable “cold shutdown” sometime between October and January.